EL elements are generally classified into intrinsic EL elements and injection EL elements. Among them according to the operation mechanism of an injection type EL element forward bias is impressed on the p-n junction of an diode or the like, electrons and positive holes are injected into the the junction from electrodes of the both sides respectively, and light is emitted by their recombination. Generally, this EL element is a luminescence element which has a structure wherein a layer manifesting the above luminescence function is arranged between two electrodes, and by the impression of voltage between these electodes converts electric energy directly to light. Characteristics of this element lie in that the element is capable of operating in a wide driving frequency range from direct current to alternative current and moreover being drived in a low voltage, and further has a possibility of a good conversion efficiency from electricity to light and the like and a possibility that, unlike usual luminescence elements such as incandescent lamps and fluorescent lamps, there can be realized face-shaped emitters, for example, thin film panels; display members, for example, of lines, drawings, images or the like having various shapes such as belt shape a cylindrical shape; panels having a large area; etc.
As materials for these injection EL elements, there have hitherto been used mainly inorganic semiconductor materials such as GaP. On the other hand, there has recently been reported an injection luminescence diode element wherein an organic compound thin film having a positive hole conductivity and an organic compound thin film having an electron conductivity are superposed into two layers [C. W. Tang: Appl. Phys. Lett. 51. (12). 913, (1987)].
Luminescence elements in which the organic material is used are drawing attention since they have characteristics, for example, that various thin film-forming methods can be selected and it is possible to form thin films of a large area in a good accuracy.
However, when an element is formed only using organic materials for EL known at present, there arise problems, for example, that the intensity of luminescence is limited in some extent and luminous intensity is unstable, and thus it is the present state of things that such an element does not come to be put to practical use. Thus, EL elements are now strongly desired about which it is possible to prepare uniform thin films having a large area and which are fertile in mass productivity and advantageous in cost face.
As a result of vigorous investigations, the present inventors have created an EL element which solves the above problems, and is fertile in mass productivity and advantageous in cost face and about which it is possible to prepare uniform thin films having a large area.
That is, the present inventors have paid their attention to the facts that the injection amount of a carrier has relation to mobility of the carrier and the mobility is higher in an organic substance than in an inorganic substance, and that a semiconductor type inorganic material has conveniences, for example, that by modulating its composition energy levels of the valence band and conduction band can be changed and controlled; have found that the above problems are solved by adopting a device constitution wherein a specific inorganic substance and a specific organic substance are joined; and have completed this invention. Such a combination of an inorganic substance and an organic substance has hitherto not been known at all. In the usual techniques, there have been used only intimate combinations of an organic substance with an organic substance, or an inorganic substance with an inorganic substance. In this point, this invention is utterly different from the usual ones in technical idea.